DESCRIPTION (as provided by Applicant): The main goal of this proposal is to answer several unresolved fundamental questions regarding the structure and function of glutamate transporters. A series of experiments have been proposed to characterize the oligomeric structure of the functional transporters and to elucidate the structural features involved in subunit assembly and substrate selectivity. Specific aim 1 will characterize the oligomeric structure of glutamate transporters and will utilize the differences between transporter subtypes to map domains necessary for subunit assembly. In addition, heteromultimerization of neuronal specific transporters will be examined. This is a critical experiment since it has been shown that EAAT3 and EAAT4 neuronal transporters are expressed together in the Purkinje cells of cerebellum. The mutagenesis and biochemical techniques described in this proposal will determine the amino acid residues necessary for substrate selectivity among transporters. In specific aim 3, bacterial glutamate transporter will be purified in order to obtain x-ray diffractable crystals. Elucidating the molecular mechanisms underlying glutamate transporter function is essential in understanding synaptic transmission.